Smart tag changes color to tell when food goes bad

Those doubtful of the validity of expiration dates may soon have an alternative to smelling their food to determine if it is still edible or not.

Natalie Crofts

DALLAS - Those doubtful of the validity of expiration dates may soon have an alternative to smelling their food to determine if it is still edible or not.
Researchers presented a tiny tag the size of a kernel of corn that can tell users how fresh their food is at the National Meeting and Exposition of the American Chemical Society Monday. The tag would appear on food and medication packaging and change colors based on the conditions the product is exposed to.
"This tag, which has a gel-like consistency, is really inexpensive and safe, and can be widely programmed to mimic almost all ambient-temperature deterioration processes in foods," lead researcher Chao Zhang said in a statement.
One of the advantages of the tag is that grocery store owners and consumers alike could know if the food had unexpectedly been exposed to high temperatures and spoiled before the expiration date, Zhang said. The colors of the tag indicate the freshness of the food, ranging from 100 percent fresh to 100 percent spoiled.
"In our configuration, red, or reddish orange, would mean fresh," Zhang said. "Over time, the tag changes its color to orange, yellow and later green, which indicates the food is spoiled."
The researchers first created the tag to determine when milk has expired, but said it can be adapted for other food items, beverages and even medications based on what conditions each product can withstand.
They said the tags would be inexpensive to make, costing about $0.002 per tag and just slightly more for food suppliers. The tags are made out of metallic nanorods and other nontoxic chemicals like vitamin C.
"Over time, the metallic silver gradually deposits on each gold nanorod, forming a silver shell layer," Zhang said. "That changes the particle's chemical composition and shape, so the tag color now would be different. Therefore, as the silver layer thickens over time, the tag color evolves from the initial red to orange, yellow, and green, and even blue and violet."
Preliminary results have been published in ACS Nano and the technique has been patented in China.%3Cimg%20src%3D%22http%3A//beacon.deseretconnect.com/beacon.gif%3Fcid%3D155159%26pid%3D46%22%20/%3E